The invention relates to a feeler pin having an optical contact sensor.
It is known, particularly for 3D measuring machines, to use a contact detecting apparatus or feelers having a feeler pin, which upon contact with a test object, experiences a deflection from which a signal is derived, in order to detect even the most infinitesimal deflections.
In this regard, it is known from German Patent No. 2,937,431, U.S. Pat. No. 4,453,082 and U.S. Pat. No. 4,574,199 that an optical system which has a light source, a mechanically influenced optical element and a light detector can detect a contact. This light source generates a stable luminous flux, which is deflected or blanked out by the optical element, so that the position and/or intensity of the light bundle arriving at the light detector thereafter are influenced.
The U.S. publications teach the use of photodiode arrays as light detectors, whereby a quantitative measurement of the magnitude of the deflection of the contact element, "measuring probe head" is also rendered possible. It is also known from U.S. Pat. No. 4,453,082 that a semiconductor laser diode can be used as a light source.
In the arrangement according to German Patent No. 2,937,431, a mirror is set oscillating by abutting the contact element on the test object. The result of this is that a stationary contact or a deformation of the feeler pin are not detected.
The measurement of changes in position with a laser diode feedback interferometer is known from U.S. Pat. No. 4,655,597 and T. Yoshino et al., Appl. Optics 26 (1987), pages 892-897. In this process, the light emitted by a laser diode is redirected by a mirror onto the laser diode. The mirror therefore acts as a third cavity facet of a combined resonator, which additionally also contains the two end mirrors of the laser diode. A change in the position of the third cavity facet with respect to the laser diode effects a change in the quality of this combined resonator. That is to say, the light emission of the laser diode is influenced by the position of the third resonator. The luminous flux of the laser diode is detected by a photodiode. A control circuit regulates the electrical operating current of the laser diode to stabilize or stably modulate the light emission. Consequently, a relative measurement of position over several .mu.m can be done with a linear signal in an experimental setup such as that shown in T. Yoshino et al. Neither of the publications describes the effects of tilting the mirror.
It is also known from R. 0. Miles et al., J. Lightwave Technology, Vol. 1, No. 1, March 1983, pages 81-93, how to use an optical sensor with a laser diode and an external near-field cavity in order to detect a deflection. In that case, the spacing of the external reflector from the resonator of the laser diode is small by comparison to the length of the resonator, so that the acceleration sensor detects even small angular tiltings of the external reflector.